Underwater detection device

ABSTRACT

An underwater detection device includes a transceiver module for transmitting underwater an ultrasonic pulse signal that is frequency-modulated and receiving an echo signal corresponding to the transmitted signal, a pulse compression module for pulse-compressing the signal received by the transceiver module and outputting a signal pulse-compressed, a suppression range determining module for determining a suppression range where a range side lobe suppression process is performed for the pulse-compressed signal, an echo determining module for determining whether the data of the pulse-compressed signal at each depth corresponding to a range side lobe, a suppression value determining module for determining a suppression value for the data of the pulse-compressed signal at each depth, a suppression conducting module for performing a calculation to suppress the range side lobe based on the suppression value for the data determined to be data of the pulse-compressed signal corresponding to the range side lobe by the echo determining module among a plurality of data of the pulse-compressed signals that fall into the suppression range, and a display processing module for generating a signal for display based on the signal outputted from the suppression conducting module to display a generated signal as detected information.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims priority under 35 U.S.C. §119 to Japanese PatentApplication No. 2008-148737, which was filed on Jun. 6, 2008, the entiredisclosure of which is hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to an underwater detection device thattransmits a frequency-modulated transmission pulse signal, receives asignal reflected from a target object, and carries out a pulsecompression process of the received signal, and more particularly, to anunderwater detection device having a configuration to remove range sidelobes produced in association with the pulse compression.

BACKGROUND

For fishfinders that is one type of underwater detection devices,increasing in detection distance is demanded to detect a shoal of fishat a deeper location. In order to increase the detection distance,generally, a transmission pulse length is simply lengthened. However, ifthe transmission pulse length is lengthened, an echo reflected from atarget object will also be longer, and the axial resolving power will bereduced. Thus, a method of increasing the axial resolving power may beadopted in which a transmission pulse is frequency-modulated, and areceived echo signal and a replica waveform of the transmitted signal iscorrelation-processed to perform a pulse compression of the receivedsignal. An underwater detection device that performs such a pulsecompression process is disclosed in JP2005-249398(A).

However, in the underwater detection device that performs the pulsecompression process, as shown in FIG. 10, false images referred to as“range side lobes” appear at positions before and after a main lobe,that shows a position of a detection target object, of apulse-compressed signal.

When the range side lobes appear, especially due to a seabed, the falseimages may be mistakenly viewed by an operator as a target object, suchas a school of small fish. In addition, an image of a shoal of fishlocated near the seabed may be difficult to view and a seabed depth maymistakenly be determined.

SUMMARY

The present invention provides an underwater detection device thatsuppresses range side lobes due to a seabed to clearly display adetection image of near the seabed.

According to an aspect of the invention, an underwater detection deviceincludes a transceiver module for transmitting underwater an ultrasonicpulse signal that is frequency-modulated and receiving an echo signalcorresponding to the transmitted signal, a pulse compression module forpulse-compressing the signal received by the transceiver module andoutputting a signal pulse-compressed, a suppression range determiningmodule for determining a suppression range where a range side lobesuppression process is performed for the pulse-compressed signal, anecho determining module for determining whether the data of thepulse-compressed signal at each depth corresponding to a range sidelobe, a suppression value determining module for determining asuppression value for the data of the pulse-compressed signal at eachdepth, a suppression conducting module for performing a calculation tosuppress the range side lobe based on the suppression value for the datadetermined to be data of the pulse-compressed signal corresponding tothe range side lobe by the echo determining module among a plurality ofdata of the pulse-compressed signals that fall into the suppressionrange, and a display processing module for generating a signal fordisplay based on the signal outputted from the suppression conductingmodule to display a generated signal as detected information.

According to the aspect of the present invention, the underwaterdetection device can be realized in which the range side lobes due tothe seabed is suppressed and the detection image of near the seabed isclearly displayed.

The suppression range determining module may include a forward peak-holdmodule that selects, for each depth, data with the largest signalstrength among data of the pulse-compressed signals falling into a depthrange from the depth concerned to a depth deeper by a predetermineddepth, and outputs the selected data as a forward peak-hold value of thedepth concerned, and a rearward peak-hold module that selects, for eachdepth, data with the largest signal strength among data of thepulse-compressed signals falling into a depth range from the depthconcerned to a depth shallower by the predetermined depth, and outputsthe selected data as a rearward peak-hold value of the depth concerned.The suppression range determining module may determine a depth rangewhere the forward peak-hold value is greater than a first predeterminedthreshold and the rearward peak-hold value is less than the firstpredetermined threshold, as the suppression range.

When a value obtained by dividing the forward peak-hold value by thedata of the pulse-compressed signal at the same depth is greater than asecond predetermined threshold, the echo determining module maydetermine the data concerned to be data corresponding to a range sidelobe.

The suppression value determining module may determine the suppressionvalue based on a suppression offset value defined with a first averagevalue derived based on data of the pulse-compressed signal within thesuppression range and a second average value derived based on data ofthe pulse-compressed signal outside the suppression range but within apredetermined depth range, and a suppression function that is a functionsimulating a shape of a range side lobe.

According to another aspect of the invention, a ship may be equippedwith any one of the underwater detection devices described above.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is illustrated by way of example and not by wayof limitation in the figures of the accompanying drawings in which thelike reference numerals indicate like elements and in which:

FIG. 1 is a block diagram of a fishfinder according to an embodiments ofthe present invention;

FIG. 2 is a block diagram showing a configuration example of a rangeside lobe suppression module;

FIG. 3 is a block diagram showing a configuration example of asuppression range determining module;

FIG. 4 is a block diagram showing a configuration example of an echodetermining module;

FIG. 5 is a block diagram showing a configuration example of asuppression value determining module;

FIG. 6 is a waveform chart for illustrating a signal processing in thesuppression range determining module;

FIG. 7 is a waveform chart for illustrating a signal processing in theecho determining module;

FIG. 8 is a waveform chart for illustrating a signal processing in thesuppression value determining module;

FIG. 9 is a waveform chart for illustrating a signal processing in asuppression conducting module; and

FIG. 10 is a waveform chart for illustrating range side lobes producedin association with a pulse compression.

DETAILED DESCRIPTION

An embodiment in which the present invention is applied to a fishfinderis explained referring to the appended drawings.

FIG. 1 is a block diagram of the fishfinder according to thisembodiment. As shown in FIG. 1, a transducer 1 typically provided at thebottom of a ship is driven by an electric signal supplied from atransmission module 3 via a trap circuit 2 to transmit an ultrasonicpulse signal to underwater and receive an echo reflected and returnedfrom an underwater target object. The transducer 1 then outputs thereceived signal to an amplifier 4 via the trap circuit 2.

The amplifier 4 amplifies the received signal, and the A/D converter 5samples the amplified signal and converts it into a digital signal. Apulse compression module 6 performs a cross correlation process with thedigital signal from the A/D converter 5 and a replica waveform of thetransmission pulse signal, and then outputs the pulse-compressed signal.A detection module 7 detects the pulse-compressed signal. A range sidelobe suppression module 8 performs a process to suppress range sidelobes for the detected pulse-compressed signal as described below. Adisplay processing module 9 generates a signal for display based on thepulse-compressed signal from the range side lobe suppression module 8the range side lobes of which are suppressed, and then displays anunderwater image on a display thereof.

FIG. 2 shows a particular configuration example of the range side lobesuppression module 8. Here, the detected pulse-compressed signalinputted into the range side lobe suppression module 8 is SIGin [n] (n=0to (N−1)) and N is a data number obtained by one transmission andreception.

In FIG. 2, a suppression range determining module 10 determines a rangewhere range side lobes of the pulse-compressed signal are suppressed. Anecho determining module 11 determines whether data of thepulse-compressed signal at each depth is echo data from a detectiontarget object or data corresponding to a range side lobe. A suppressionvalue determining module 12 determines a suppression value to be usedwhen performing an operation to suppress the range side lobe for data ofthe pulse-compressed signal at each depth.

A suppression value verifying module 13 verifies whether the suppressionvalue determined by the suppression value determining module 12 is anappropriate value. A suppression ON/OFF module 14 determines whether thesuppression process of the range side lobe is to be performed for thedata at each depth based on the output result of the suppression rangedetermining module 10, the output result of the echo determining module11, and the verified result of the suppression value verifying module13. A suppression conducting module 15 performs a suppression operationof the range side lobe by giving a predetermined calculation with thesuppression value determined by the suppression value determining module12 for the data of the pulse-compressed signal at each depth based onthe determination result of the suppression ON/OFF module 14.

FIG. 3 shows a configuration example of the suppression rangedetermining module 10. In FIG. 3, a forward peak-hold module 16 selectsdata which is the largest in signal strength from the data of thepulse-compressed signals falling into a depth range from each depthconcerned to a predetermined deeper depth, respectively, and outputs theselected data as a forward peak-hold value of the depth concerned.Specifically, a forward peak-hold value MPH_F [n] (hereinafter,abbreviated as, “forward PH value”) may be generated using the followingEquation (1):MPH _(—) F[n]=max(SIGin[n+1,n+k])  (1)In Equation (1), max(SIGin [n+1,n+k]) represents data with the maximumsignal strength among the pulse-compressed signal data from SIGin [n+1]to SIGin [n+k]. The value k is a data number corresponding to theabove-described predetermined depth, and it may be desirable to be anumber substantially corresponding to a length of the transmissionpulse.

A rearward peak-hold module 17 selects data which is the largest insignal strength from the data of the pulse-compressed signals fallinginto a depth range from each depth concerned to a predeterminedshallower depth, respectively, and outputs the selected data as arearward peak-hold value of the depth concerned. Specifically, therearward peak-hold value MPH_B [n] (hereinafter, abbreviated as a“rearward PH value”) may be generated by the following Equation (2):MPH _(—) B[n]=max(SIGin[n−k+1,n])  (2)

The suppression range setting module 18 sets a suppression range to arange where the forward PH value exceeds a predetermined threshold(first threshold) and the rearward PH value does not exceed thethreshold.

FIG. 6 shows a particular example in which the forward PH value and therearward PH value are calculated for the detected pulse-compressedsignal and the suppression range is set based on the threshold. In FIG.6, the first threshold is set to 120 dB, and a solid line represents thepulse-compressed signal, a dashed dotted line represents the forward PHvalue, and a two dotted line represents the rearward PH value.

Alternatively, the suppression range determining module 10 may have aconfiguration in which a pulse-compressed signal is compared with apredetermined threshold, and a range from a position at which thepulse-compressed signal exceeds the threshold to a position shallower bythe transmission pulse length is set to be the suppression range.Further, the suppression range determining module 10 may have aconfiguration in which a range from a seabed position derived by a knownseabed detecting method to a position shallower by the transmissionpulse length is set to be the suppression range.

FIG. 4 shows a configuration example of the echo determining module 11.A forward peak-hold module 19 has the same function as the forwardpeak-hold module 16 of FIG. 3. The forward peak-hold modules 16 and 19may also be configured as a single common module having both functions.A division module 20 divides the data MPH_F [n] of the forward PH valueat each depth by the value SIGin [n] of the pulse-compressed signal atthe depth concerned. A comparison module 21 compares the output resultof the division module 20 with a predetermined threshold (secondthreshold). The comparison module 21 determines the data to be an echofrom the detection target object when the output value is less than thesecond threshold, and determines the data concerned to be datacorresponding to a range side lobe when the output value is greater thanthe second threshold.

FIG. 7 shows a waveform chart of each signal in the echo determiningmodule 11 for the same received data as FIG. 6. In FIG. 7, a graph witha dotted line represents a signal generated in the division module 20.In FIG. 7, the second threshold is set to approximately 50 dB, and datain ranges other than an echo from a shoal of fish at a seabed isdetermined to be suppressed.

FIG. 5 shows a configuration example of the suppression valuedetermining module 12. A suppression offset value calculating module 22divides an average value derived from a plurality of data within thesuppression range (“first average value”) by an average value calculatedfrom data in a predetermined depth range other than the suppressionrange (“second average value”). The second average value may becalculated from data, for example, in a depth range from a startingposition of the suppression range (e.g., an end portion on the shallowerside of the suppression range) to a position shallower by thetransmission pulse length. The suppression offset value calculatingmodule 22 then outputs the division result as a suppression offsetvalue. It may be desirable to exclude data greater than a predeterminedlevel in the calculation of the first average value and the secondaverage value.

A suppression value calculating module 23 stores in advance a functionsimulating a standard range side lobe shape that may be obtained byexperiments as a suppression function. The suppression value calculatingmodule 23 calculates a suppression value for each data based on afunction produced multiplying the suppression function by thesuppression offset value calculated by the suppression offset valuecalculating module 22.

FIG. 8 shows the calculated results of the first average value, thesecond average value, the suppression offset value, and the suppressionvalue by the suppression value determining module 12 for the samereceived data as FIG. 6.

The suppression value verifying module 13 verifies whether thesuppression value determined by the suppression value determining module12 is an appropriate value. Specifically, the suppression valueverifying module 13 verifies whether or not a suppression value whichincreases range side lobes in the calculation by the suppressionconducting module 15 (division of each data by the suppression value) isan inappropriate suppression value (less than 1).

Based on the respective output results from the suppression rangedetermining module 10, the echo determining module 11, and thesuppression value verifying module 13, the suppression ON/OFF module 14determines the suppression process for the data concerned to beperformed, when the data falls into the suppression range andcorresponds to the range side lobe and when an appropriate suppressionvalue is calculated for the data concerned.

A suppression conducting module 15 performs a division of the data to besuppressed by the suppression value based on the determination result ofthe suppression ON/OFF module 14, and outputs it to the displayprocessing module 9. The suppression conducting module 15 otherwiseoutputs data not to be suppressed to the display processing module 9without performing the division.

FIG. 9 is a waveform chart resulting from the range side lobesuppression process performed in the suppression conducting module 15for the same received data as FIG. 6. It can be seen that sections thatfall into the range side lobes, due to the seabed, are suppressedwithout the echo signal from the target object near the seabed beingweakened.

As described above, although the fishfinder was described as an example,the present invention may also be applied to other underwater detectiondevices, such as scanning sonar, PPI sonar, etc. In the aboveembodiment, the intended application is at sea; however, any waterapplication may be possible within the scope of the invention.

In the foregoing specification, specific embodiments of the presentinvention have been described. However, one of ordinary skill in the artappreciates that various modifications and changes can be made withoutdeparting from the scope of the present invention as set forth in theclaims below. Accordingly, the specification and figures are to beregarded in an illustrative sense rather than a restrictive sense, andall such modifications are intended to be included within the scope ofthe present invention. The benefits, advantages, solutions to problems,and any element(s) that may cause any benefit, advantage, or solution tooccur or become more pronounced are not to be construed as critical,required, or essential features or elements of any or all the claims.The invention is defined solely by the appended claims including anyamendments made during the pendency of this application and allequivalents of those claims as issued.

Moreover in this document, relational terms such as first and second,top and bottom, and the like may be used solely to distinguish oneentity or action from another entity or action without necessarilyrequiring or implying any actual relationship or order between suchentities or actions. The terms “comprises,” “comprising,” “has,”“having,” “includes,” “including,” “contains,” “containing” or any othervariation thereof, are intended to cover a non-exclusive inclusion, suchthat a process, method, article, or apparatus that comprises, has,includes, contains a list of elements does not include only thoseelements but may include other elements not expressly listed or inherentto such process, method, article, or apparatus. An element proceeded by“comprises . . . a,” “has . . . a,” “includes . . . a,” “contains . . .a” does not, without more constraints, preclude the existence ofadditional identical elements in the process, method, article, orapparatus that comprises, has, includes, contains the element. The terms“a” and “an” are defined as one or more unless explicitly statedotherwise herein. The terms “substantially,” “essentially,”“approximately,” “approximately” or any other version thereof, aredefined as being close to as understood by one of ordinary skill in theart, and in one non-limiting embodiment the term is defined to be within10%, in another embodiment within 5%, in another embodiment within 1%and in another embodiment within 0.5%. The term “coupled” as used hereinis defined as connected, although not necessarily directly and notnecessarily mechanically. A device or structure that is “configured” ina certain way is configured in at least that way, but may also beconfigured in ways that are not listed.

1. An underwater detection device, comprising: a transceiver module fortransmitting underwater an ultrasonic pulse signal that isfrequency-modulated and receiving an echo signal corresponding to thetransmitted signal; a pulse compression module for pulse-compressing thesignal received by the transceiver module and outputting a signalpulse-compressed; a suppression range determining module for determininga suppression range where a range side lobe suppression process isperformed for the pulse-compressed signal; an echo determining modulefor determining whether the data of the pulse-compressed signal at eachdepth corresponding to a range side lobe; a suppression valuedetermining module for determining a suppression value for the data ofthe pulse-compressed signal at each depth; a suppression conductingmodule for performing a calculation to suppress the range side lobebased on the suppression value for the data determined to be data of thepulse-compressed signal corresponding to the range side lobe by the echodetermining module among a plurality of data of the pulse-compressedsignals that fall into the suppression range, the suppression rangedetermining module including a forward peak-hold module that selects,for each depth, data with the largest signal strength among data of thepulse-compressed signals falling into a depth range from the depthconcerned to a depth deeper by a predetermined depth, and outputs theselected data as a forward peak-hold value of the depth concerned; and arearward peak-hold module that selects, for each depth, data with thelargest signal strength among data of the pulse-compressed signalsfalling into a depth range from the depth concerned to a depth shallowerby the predetermined depth, and outputs the selected data as a rearwardpeak-hold value of the depth concerned; and a display processing modulefor generating a signal for display based on the signal outputted fromthe suppression conducting module to display a generated signal asdetected information; wherein the suppression range determining moduledetermines a depth range where the forward peak-hold value is greaterthan a first predetermined threshold and the rearward peak-hold value isless than the first predetermined threshold, as the suppression range.2. The underwater detection device of claim 1, wherein when a valueobtained by dividing the forward peak-hold value by the data of thepulse-compressed signal at the same depth is greater than a secondpredetermined threshold, the echo determining module determines the dataconcerned to be data corresponding to a range side lobe.
 3. Theunderwater detection device of claim 1, wherein the suppression valuedetermining module determines the suppression value based on asuppression offset value defined with a first average value derivedbased on data of the pulse-compressed signal within the suppressionrange and a second average value derived based on data of thepulse-compressed signal outside the suppression range but within apredetermined depth range, and a suppression function that is a functionsimulating a shape of a range side lobe.